As is well known, virtual concatenation (VC) and link capacity adjustment scheme (LCAS) protocols have been developed which allow more efficient use of the existing fixed-bandwidth connections associated with synchronous optical network (SONET) or synchronous digital hierarchy (SDH) network infrastructure. For example, these protocols are utilized in transmission of Ethernet over SONET (EoS) data traffic over metropolitan networks, and in numerous other data transmission applications. The VC and LCAS protocols are described in greater detail in, for example, ITU-T standards documents G.707 and G.7042, respectively, both of which are incorporated by reference herein.
Virtual concatenation generally allows a given source node of a network to form a virtually-concatenated group (VCG) which includes multiple members each associated with a corresponding data stream. The different data streams may then be transmitted over diverse routes through the network from the source node to a given destination node, also referred to herein as a sink node. The sink node recombines the streams to reconstruct the original VCG.
The LCAS protocol enhances the basic virtual concatenation functionality described above by allowing so-called “hitless” addition and deletion of members from a VCG, that is, addition and deletion of members without the introduction of errors into the transmitted data. The LCAS protocol also enables a VCG to operate at a reduced capacity after the failure of routes associated with one or more members, by allowing the temporary removal of members associated with failed routes from the VCG.
Conventional restoration techniques in the SONET/SDH context are designed to provide fast restoration in the event of route failure, where “fast” restoration generally denotes restoration of the associated data traffic in less than about 50 milliseconds. However, this fast restoration comes at the cost of excessive bandwidth overhead. More specifically, these conventional techniques generally utilize 1+1 primary-backup protection, wherein each primary route has a corresponding backup route, resulting in 100% bandwidth overhead.
It should also be noted that the above-described LCAS protocol takes on the order of 64 or 128 milliseconds, for respective higher order (HO) or lower order (LO) implementations, in order to complete the above-noted temporary removal of members associated with failed routes. This delay is attributable to the refresh timing mechanism of the LCAS protocol. Therefore, the LCAS protocol in its current form is unable to deliver the approximately 50 millisecond fast restoration generally associated with SONET/SDH networks. This not only precludes its use for restoration but also makes SONET 1+1 protection in conjunction with LCAS ineffective.
A possible alternative approach is to transmit the data traffic without providing any protection at the SONET/SDH layer of the network, in the expectation that higher layers, such as an Ethernet layer, will be able to provide a certain measure of protection. For example, in the case of the above-noted EoS data traffic, rapid Ethernet spanning tree protection in the Ethernet layer may be used for restoration in the event of route failure. However, this type of restoration by higher network layers can lead to a number of significant problems, such as disruption of data traffic for up to several seconds, loss and duplication of data, etc.
U.S. patent application Ser. No. 10/446,220 filed May 28, 2003 and entitled “Fast Restoration for Virtually-concatenated Data Traffic,” the disclosure of which is incorporated by reference herein, addresses the above-noted issues by providing improved techniques for protection of data traffic against route failure. Advantageously, these techniques in an illustrative embodiment are able to provide fast restoration, on the order of 50 milliseconds or less, while utilizing less than 100% bandwidth overhead. Although particularly well-suited for use with EoS data traffic, the disclosed techniques can also be used with other types of virtually-concatenated data traffic.
Despite the considerable advances provided by the techniques described in the above-cited U.S. patent application Ser. No. 10/446,220, a need remains for further improvements in protecting data traffic against route failure, and more particularly in routing algorithms that are utilized to determine appropriate restoration routes.